Inhalation toxicity studies were designed to study the toxicity and potential carcinogenicity of styrene and two congeners, alpha methylstyrene and divinylbenzene. In initial studies, B6C3F1 mice were exposed to 125, 250, or 500 ppm styrene 6 hr/day for 14 days. Male mice were more susceptible than females to styrene toxicity, and 250 ppm appeared to be more toxic than 500 ppm. The primary target organ affected by styrene inhalation was the liver. In mice that died from exposure to styrene, about 80% of the liver was necrotic. Mice that survived styrene exposure for 14 days had little evidence of liver injury, indicating that these animals recovered rapidly in spite of continued exposure. Additional experiments are underway to evaluate the mechanisms of the high susceptibility of mice to styrene, sex and strain differences, recovery and the nonlinear dose response. These studies are designed to provide scientific information on the comparative toxicity of styrene and its, congeners, and on possible mechanisms for potential carcinogenicity of these important chemicals.